基于实时超声图像引导技术和线性判别模型分析前列腺癌放疗分次内运动模式

目的 基于经会阴超声(TPUS)实时扫描技术和线性判别分析(LDA)法,定性分析并自动判别前列腺癌放疗分次内运动模式,为个体化精确放疗奠定基础。方法 应用TPUS技术记录了61例前列腺癌患者共1265个分次近百万个实时监测数据,划分为稳定型、波浪型、小偏执型、银叉型、回归型、大偏执型和稽留型运动模式。对运动轨迹量化并提取特征参数,通过LDA法建立判别方程式,评估训练集和测试集的判别效果。结果 平均每位患者存在4种不同的运动模式,不稳定型占(35.00±21.49)%。随着治疗次数的增加,运动轨迹并未表现出越来越稳定的趋势,不同模式的出现极不规则。构建的线性判别模型对训练集和测试集的判别准确率分别为90.4%和89.5%,敏感性和特异性分别为84.9%和91.1%。结论 前列腺癌患者分次内运动模式多样且随机,具有不可预测的特点。LDA法可以有效地对分次内运动模式进行判别,同时在治疗过程中利用判别方程和中心坐标实现对未知样本的自动鉴别。     

前列腺癌影像引导放疗中电子射野影像装置和经会阴超声实时位置验证方法比较

[目的]比较电子射野影像装置（electronic portal imaging device,EPID）和Clarity经会阴超声（trans-perineal ultrasound,TPUS）在基于黄金基准标志物的前列腺癌影像引导放疗（IGRT）中靶区实时位置验证效能。[方法]筛选符合标准的前列腺癌患者10例,接受治疗前锥形束CT验证以确保前列腺癌IGRT分次治疗间靶区位置准确性;之后接受治疗中实时EPID和TPUS成像,分别采用Bland-Altman法和独立样本t检验评价两种成像方法对前列腺癌IGRT分次治疗内靶区位置验证一致性和差异。[结果] TPUS和EPID位置验证数值在左右、头脚、腹背3个方向上具有中度以上相关性（r=0.879、0.645、0.531）。3个方向上TPUS位置验证数值显著性小于EPID[(0.32±0.20)mm vs (0.51±0.33) mm,(0.41±0.31) mm vs (0.63±0.48) mm,(0.46±0.38) mm vs (0.72±0.45) mm,P均<0.05]。TPUS和EPID记录的总位移时间呈弱相关（r=0...     

前列腺癌大分割精确放疗分次治疗间和分次治疗内位置变动分析

目的 了解前列腺癌精确大分割放疗时分次间和分次内前列腺靶区位移情况。方法 对 2013—2016年间28例接受5 Gy9次放疗的前列腺癌患者,定位前2周B超引导下经直肠穿刺前列腺内植入纯金标记3颗,仰卧位体膜固定充盈膀胱并直肠内插置直肠扩张球囊充气60 ml后CT定位,Pinnacle系统制定放疗计划。23例患者Synergy加速器治疗,每次疗前CBCT校位,扫描图像与计划图像行骨配准记录摆位误差,然后通过前列腺内金标位置配准记录前列腺位移误差,两次之差为分次间位移。5例患者Novalis加速器治疗,通过前列腺内金标配准,疗中ExacTrac系统实时跟踪金标位置变化,观察前列腺分次内位移。结果 23例患者每次疗前均测量位移共计207次,左右、上下、前后位移平均值分别为(0.05±0.10)、(0.20±0.22)、(0.19±0.18) cm;3个方向>0.3 cm位移分别为1、52、49次,>0.5 cm位移分别为1、29、16次。5例患者每次疗时监测测量金标位置移动5次共计225次,左右、上下、前后位移平均值分别为(0.61±0.50)、(0.68±0.69)、(0.70±0.67) mm,各方向>3 mm移动分别为0、1、1次。结论 前列腺癌精确大分割放疗时分次间位移远远大于分次内位移,分次间位移必须校正后才能放疗。分次内靶区位移尽管变化较小,但仍有必要监测分次内靶区位移,以防患者体位变动造成靶区脱靶照射。直肠内球囊插入对前列腺位置具有固定作用。     

分次内锥形束CT在前列腺癌术后放疗中的运用

目的;分析分次内锥形束 CT（cone beam computed tomography,CBCT）的质量,利用分次内 CBCT 分析前列腺放疗中的分次内误差。方法;采用模体验证、分次间半弧、分次间全弧及分次内 CBCT扫描模式扫描 CTP 503 Phantom,分析 CBCT 图像的几何、空间分辨率、低对比度及均匀性。纳入 14 例前列腺切除术后放疗患者,扫描分次间 CBCT后纠正误差,在治疗过程中进行分次内 CBCT扫描,分析前列腺癌患者放疗中分次内误差。结果∶模体验证模式扫描的空间分辨率、低对比度及均匀性均优于其他模式。相比分次间半弧、分次间全弧扫描模式,分次内 CBCT存在明显的伪影,空间分辨率为3 个线对,低对比度为1.52,均匀性为 3.57%。分次间半弧及分次内 CBCT均不能清晰显示前列腺瘤床轮廓。前列腺放疗中分次内系统误差与随机误差为在左右方向（medial-to-lateral,ML）0.5 mm/ 0.6 mm,在头脚方向（superior-to-inferior,S）0.8 mm/0.5 mm,在胸腹方向（anterior-to-posterior,AP）0.7mm/0.6 mm,相应的计划靶区（planning target volume,PTV）边界为1.67mm（ML）,2.35 mm（SI）与2.17mm（AP）。结论∶兆伏射线对分次内 CBCT 的影响主要表现在散射伪影,常规分次间 CBCT 及分次内 CBCT 均不能清晰显示前列腺瘤床。 CBCT纠正后的残余误差及治疗中患者的移动小,5 mm 的 PTV 边界能够补偿前列腺癌术后放疗的位置误差。     

深吸气屏气和自由呼吸状态在乳腺托架固定下全乳调强放疗中的摆位误差研究

目的 比较乳腺癌保乳术后深吸气屏气(DIBH)与自由呼吸(FB)状态下放疗的摆位误差。方法 回顾性分析 2016年4月至 2018年6月在中国医学科学院肿瘤医院接受保乳术后采用DIBH技术行全乳放疗的左侧乳腺患者 30例,并选取 30例自由呼吸状态下接受全乳放疗的乳腺癌患者作为对照。比较放疗计划系统CT图像与放射治疗期间锥形束CT的位移,确定摆位误差,并计算临床靶体积(CTV)外扩至计划靶体积(PTV)的边界。摆位误差的比较采用t检验。结果 全组患者共拍摄锥形束CT图像318套,平均每人(5.1±1.1)套。FB患者摆位误差在x轴、y轴和z轴的位移分别为(2.2±1.7) mm,(3.1±2.5) mm,(3.3±2.3) mm。DIBH患者摆位误差在x轴、y轴和z轴的位移分别为(2.1±1.6) mm,(2.6±1.7) mm,(2.5±2.1) mm。在y轴和z轴方向,DIBH患者的位移显著小于FB患者(P=0.015、0.004),两组患者在x轴方向位移无明显差别(P=0.294)。DIBH患者CTV至PTV在x轴、y轴和z轴方向外扩边界分别为6.2、7.3、7.8mm。DIBH组放疗第一周与后续放疗、不同体重指数(BMI)的摆位误差无差别。结论 乳腺癌保乳术后全乳放疗时,DIBH技术摆位误差小于FB,推荐DIBH放疗的CTV至PTV的外扩边界为 6~8mm。     

颈段、胸上段食管癌容积弧形调强放疗与固定野调强放疗分次内误差的比较

目的 分析颈段、胸上段食管癌容积弧形调强放疗（VMAT）和固定野调强放疗（IMRT）的分次内误差,比较两种治疗技术在减少摆位误差方面的优劣。方法 收集2013年6月至2014年12月在我科接受VMAT与IMRT的颈段、胸上段食管癌患者各25例,所有患者分别在每次治疗摆位纠正前、摆位纠正后及治疗后行锥形束CT（CBCT）并与计划CT匹配,获取分次内误差,对两种治疗技术进行对比分析。结果 IMRT组在X（左右）、Y（头脚）、Z（腹背）3个轴方向的摆位纠正后误差分别为（0.63±0.47）mm、（0.84±0.35）mm、（0.67±0.41）mm,治疗后误差依次为（1.01±0.42）mm、（1.08±0.89）mm、（1.07±0.70）mm,治疗后误差高于纠正后误差,差异有统计学意义（P＜0.05）;VMAT组在X、Y、Z 3个轴方向的摆位纠正后误差分别为（0.62±0.50）mm、（0.78±0.40）mm、（0.72±0.54）mm,治疗后误差依次为（0.71±0.52）mm、（0.84±0.41）mm、（0.79±0.63）mm,治疗后误差略高于纠正后误差,差异无统计学意义（P＞0.05）。1～6周每周获得的分次内误差,随着治疗周数的增多,两组各方向的平均误差均有所增加,且IMRT组数据高于VMAT组,差异有统计学意义（P＜0.05）。VMAT组的治疗时间和加速器跳数为（2.85±0.73）min和589.00±63.00,均优于IMRT组的（8.14±1.06）min和792.00±83.00,差异有统计学意义（P＜0.05）。结论 在颈段、胸上段食管癌的放疗中,VMAT能大大缩短治疗时间,减少治疗中不确定因素的影响和患者不舒适度,有效降低患者分次内误差,但放疗分次内误差仍随着治疗时间延长逐渐增大。     

前列腺癌放疗中前列腺体积缩小与新辅助内分泌治疗时间的关系研究

目的 探讨前列腺癌放疗中体积变化与新辅助内分泌治疗(NHT)之间的关系。方法 55例接受NHT前列腺癌患者连续入组,放疗中每周测量前列腺左右、上下、前后方向直径并计算体积。分析放疗中前列腺缩小与NHT时间、放疗前体积及前列腺癌风险分组间关系。结果 所有患者前列腺体积均随放疗进行而减小,NHT时间短者各项变化幅度大于时间长者。前列腺体积正常组与增大组比,前者在放疗7周后体积变化比例及各方向直径变化幅度均较大,且放疗前NHT时间较短,前列腺癌风险较低。与放疗前相比,中低危患者NHT≤4个月的体积分别缩小至68.10%、78.70%(P=0.002),而>4个月者变化较微弱;高危以上患者NHT≤6个月的体积分别缩小至76.59%及85.46%(P=0.001),而>6个月者相近。结论 NHT时间越长,放疗中前列腺体积及各方向直径变化幅度越小。中低危前列腺癌患者NHT4个月以后前列腺体积的变化幅度较小,高危或局部进展期患者NHT时间6个月以后变化幅度较小。     

二维电离室矩阵实时验证VMAT剂量价值研究

目的 探讨利用二维电离室矩阵进行VMAT患者透射剂量实时验证的临床价值。方法 将二维电离室矩阵面板粘贴固定在加速器EPID探测面板上,源到EPID探测面板距离为140 cm。电离室矩阵面板上加8 mm的RW3固体水以提高信躁比。选取食管癌、前列腺癌、肝癌患者计划,在圆柱形Cheese模体上照射测量5次,研究患者计划在模体中剂量验证的可行性与准确性。患者每次治疗时进行实时测量,第1次测量结果作为参考剂量,利用γ分析比较分次间剂量误差。结果采用3%3 mm标准,Cheese模体VMAT计划的γ通过率为98%左右,食管癌、前列腺癌和肝癌患者实时照射γ通过率分别约为92%、92%和94%。整个治疗过程中各分次的γ通过率都在90%以上。     

不同放疗方法在胸腹部的移动特点比较

目的 探讨放疗过程中胸部和腹部的移动特点。方法 选取2016年2—7月四川省肿瘤医院接受放疗的120例患者,胸、腹部各60例。在放疗过程中采用Sentinel系统实时监测并记录患者2种治疗部位体表轮廓的移动数据,分析其移动特点。配对t检验差异。结果 胸、腹部移动类型主要包括基本不动型、移动稳定型、跳跃型及逐渐增加型4种,分别占14.0%、64.0%、8.7%和13.3%。治疗部位偏移值:胸部IMRT (6.55±2.34) mm和VMAT (4.97±1.24) mm (P=0.002),腹部IMRT (3.97±1.80) mm和VMAT (2.69±1.42) mm (P=0.004)。胸、腹偏移值随治疗时间的延长而增加,同一时间段内胸部的偏移值高于腹部。结论 对于胸部和腹部接受放疗的患者,治疗部位的移动是普遍存在的。VMAT技术能有效降低胸腹部的偏移值,确保治疗剂量的准确性。     

胃癌术后放疗中呼吸运动及主动呼吸控制对靶区移动影响分析

目的 了解胃癌术后放疗患者中自由呼吸运动对放疗靶区移动程度,分析采用主动呼吸控制(ABC)方法后靶区移动程度及相关因素.方法 22例胃癌患者术中在瘤床或淋巴结引流区放置银夹作为标记,术后采用ABC技术定位放疗.每周重复2次采集自由呼吸和ABC时相0°和90°图像,应用Image J图像处理软件处理图像及标记银夹.测定自由呼吸和采用ABC时银夹在头脚、左右及前后轴向上的移动幅度,包括同次放疗内和分次放疗间移动幅度.结果 自由呼吸和采用ABC后头脚、左右、前后轴向上的移动幅度分别为11.1、1.9、2.5 mm(F=85.15,P=0.000)和2.2、1.1、1.7 mm(F=17.64,P=0.000),头脚、前后方向明显减少(t=4.36,P=0.000;t=3.73,P=0.000);同次放疗内自由呼吸与ABC后同一呼吸相内的无变化,而ABC后异次呼吸相内的分别为3.7、1.6、2.8mm(F=19.46,P=0.000),3个方向均明显增加(t=-4.36,P=0.000;t=-3.52,P=0.000;t=-3.79,P=0.000);ABC后分次放疗间的银央簇中心和银夹最大移动幅度分别为2.7、1.7、2.5 mm(F=4.07,P=0.019)和4.6、3.1、4.2 mm(F=5.17,P=0.007),3个方向均明显增加(t=-4.09,P=0.000;t=-4.46,P=0.000;t=-3.45,P=0.000).结论 胃癌术后自由呼吸状态下放疗靶区移动幅度以头脚方向最大,左右方向最小;采用ABC技术后头脚、前后方向明显减小,而同次治疗内和分次放疗问的也有类似变化.     

Evaluation of intrafraction prostate motion tracking using the Clarity Autoscan system for safety margin validation

BackgroundThe purpose of the study was to monitor intrafraction prostate motion in real-time using transperineal 4D ultrasound (TPUS) and analyze trajectories to validate clinical safety margins.Methods401 trajectories of US monitoring sessions were retrospectively evaluated for 14 patients treated for prostate cancer. The Elekta Clarity Autoscan system was used for intrafraction monitoring along the 3 directions: superior-inferior (SI), left-right (LR) and anterior-posterior (AP).ResultsThe intrafraction monitoring resulted in a mean prostate displacement of (-0.06 ± 0.49) mm, (-0.09 ± 0.61) mm and (-0.01 ± 0.78) mm in the SI, LR and AP directions, respectively. Even though large deviations up to 8 mm were detected, the frequency of occurrence was less than 0.1%. The prostate moved within ±2 mm in 99%, 98.1%, and 96.6% of the treatment time in the SI, LR and AP directions, respectively. During 100 s of monitoring, the median displacement increased from 0.2 mm to 0.8 mm and the maximum displacements increased from 5.2 mm to 7.8 mm. The majority of displacement values (99%) were within the clinical safety margins which ensures a good target coverage.ConclusionsThe largest variation of intrafraction prostate displacement was observed along the AP direction. Throughout most of the treatment time, the prostate moved within a few millimeters. The extent of prostate displacement increased for longer monitoring times. During most of the tracking time, the prostate position was within the clinically safety margins.     

Clinical assessment of the use of the Sonarray system for daily prostate localization.

The Sonarray ultrasound system is a non-invasive technique allowing real-time prostate localization. Since 2003, it has been used in our department before intensity modulated radiation therapy for prostate cancer. We reported both setup errors and organ motion detected by Sonarray system and the accuracy of this ultrasound imaging dedicated to radiotherapy.     

Large prostate motion produced by anal contraction

BACKGROUND AND PURPOSE: The aim of this study was to define the effects of voluntary anal contraction on prostate motion in an experimental setting. MATERIALS AND METHODS: Thirty-eight patients (median age, 76years) with prostate cancer underwent thin-slice computed tomography (CT) in the vicinity of the prostate before and after active anal contraction. Three-dimensional displacement of the pelvis and prostate was measured. RESULTS: Mean (±standard deviation, SD) overall displacement of the prostate due to anal contraction was 0.3±1.4mm to the right, 9.3±7.8mm to the anterior, and 5±4mm to the cranial direction. Mean displacement of the pelvis was 0.5±1.8mm to the right, 4.1±7.1mm to the anterior, and 1±3mm to the cranial direction. Mean displacement of the prostate relative to the pelvis was 0.1±1.1mm to the left, 5.2±3.3mm to the anterior, and 4±4mm to the cranial direction. CONCLUSIONS: Voluntary anal contraction within an experimental setting induces large prostate and bone motion, mainly in the anterior and cranial directions. The frequency and magnitude of actual anal contractions during radiotherapy for prostate cancer need to be determined.     

Online ultrasound image guidance for radiotherapy of prostate cancer: impact of image acquisition on prostate displacement

AIM: Numerous studies reported the use of ultrasound image-guidance system to assess and correct patient setup during radiotherapy for prostate cancer. We conducted a study to demonstrate and quantify prostate displacement resulting from pressure of the probe on the abdomen during transabdominal ultrasound image acquisition for prostate localization. MATERIAL AND METHODS: Ten healthy volunteers were asked to undergo one imaging procedure. The procedure was performed in a condition that simulates the localization of prostate during online ultrasound guidance. A 3D ultrasound machine was used. The procedure started with the placement of the probe on the abdomen above the pubis symphysis. The probe was tilted in a caudal and posterior direction until the prostate and seminal vesicle were visualized. The probe was then fixed with a rigid arm, which maintained the probe in a static position during image acquisition. The probe was then moved, in a short time, stepwise toward the prostate, acquiring images at each step. The prostate and seminal vesicles were identified and selected in all planes. The first 3D volume was used as reference 1, to which all other scans were matched using a gray value matching algorithm. RESULTS: Prostate motion was quantified as a 3D translation relative to the patient coordinate system. The resulting translations represented the amount of prostate movement as a function of probe displacement. Between 7 and 11 images were obtained per volunteer, with a maximal probe displacement ranging between 3 and 6 cm. Prostate displacement was measured in all volunteers for all the probe steps and in all directions. The largest displacements occurred in the posterior direction in all volunteers. The absolute prostate motion was less than 5 mm in 100% of the volunteers after 1 cm of probe displacement, in 80% after 1.5 cm, in 40% after 2 cm, in 10% after 2.5 cm, and 0% after 3 cm. To achieved a good-quality ultrasound images, the probe requires an average displacement of 1.2 cm, and this results in an average prostate displacement of 3.1 mm. No correlations were observed between prostate motion and prostate-probe distance or bladder size. CONCLUSION: Probe pressure during ultrasound image acquisition causes prostate displacement, which is correlated to the amount of probe displacement from initial contact. The induced uncertainty associated with this process needs to be carefully evaluated to determine a safe margin to be employed during online ultrasound image-guided radiotherapy of the prostate.     

Positioning errors and prostate motion during conformal prostate radiotherapy using on-line isocentre set-up verification and implanted prostate markers.

PURPOSE: To evaluate treatment errors from set-up and inter-fraction prostatic motion with port films and implanted prostate fiducial markers during conformal radiotherapy for localized prostate cancer. METHODS: Errors from isocentre positioning and inter-fraction prostate motion were investigated in 13 men treated with escalated dose conformal radiotherapy for localized prostate cancer. To limit the effect of inter-fraction prostate motion, patients were planned and treated with an empty rectum and a comfortably full bladder, and were instructed regarding dietary management, fluid intake and laxative use. Field placement was determined and corrected with daily on-line portal imaging. A lateral portal film was taken three times weekly over the course of therapy. From these films, random and systematic placement errors were measured by matching corresponding bony landmarks to the simulator film. Superior-inferior and anterior-posterior prostate motion was measured from the displacement of three gold pins implanted into the prostate before planning. A planning target volume (PTV) was derived to account for the measured prostate motion and field placement errors. RESULTS: From 272 port films the random and systematic isocentre positioning error was 2.2 mm (range 0.2-7.3 mm) and 1.4 mm (range 0.2-3.3 mm), respectively. Prostate motion was largest at the base compared to the apex. Base: anterior, standard deviation (SD) 2.9 mm; superior, SD 2.1 mm. Apex: anterior, SD 2.1 mm; superior, SD 2.1 mm. The margin of PTV required to give a 99% probability of the gland remaining within the 95% isodose line during the course of therapy is superior 5.8 mm, and inferior 5.6 mm. In the anterior and posterior direction, this margin is 7.2 mm at the base, 6.5 mm at the mid-gland and 6.0 mm at the apex. CONCLUSIONS: Systematic set-up errors were small using real-time isocentre placement corrections. Patient instruction to help control variation in bladder and rectal distension during therapy may explain the observed small SD for prostate motion in this group of patients. Inter-fraction prostate motion remained the largest source of treatment error, and observed motion was greatest at the gland base. In the absence of real-time pre-treatment imaging of prostate position, sequential portal films of implanted prostatic markers should improve quality assurance by confirming organ position within the treatment field over the course of therapy.     

Intrafraction prostate motion during IMRT for prostate cancer

PURPOSE: Although the interfraction motion of the prostate has been previously studied through the use of fiducial markers, CT scans, and ultrasound-based systems, intrafraction motion is not well documented. In this report, the B-mode, Acquisition, and Targeting (BAT) ultrasound system was used to measure intrafraction prostate motion during 200 intensity-modulated radiotherapy (IMRT) sessions for prostate cancer. METHODS AND MATERIALS: Twenty men receiving treatment with IMRT for clinically localized prostate cancer were selected for the study. Pre- and posttreatment BAT ultrasound alignment images were collected immediately before and after IMRT on 10 treatment days for a total of 400 BAT alignment procedures. Any ultrasound shifts of the prostate borders in relation to the planning CT scan were recorded in 3 dimensions: right-left (RL), anteroposterior (AP), and superior-inferior (SI). Every ultrasound procedure was evaluated for image quality and alignment according to a 3-point grading scale. RESULTS: All the BAT images were judged to be of acceptable quality and alignment. The dominant directions of intrafraction prostate motion were anteriorly and superiorly. The mean magnitude of shifts (+/-SD) was 0.01 +/- 0.4 mm, 0.2 +/- 1.3 mm, and 0.1 +/- 1.0 mm in the left, anterior, and superior directions, respectively. The maximal range of motion occurred in the AP dimension, from 6.8 mm anteriorly to 4.6 mm posteriorly. The percentage of treatments during which prostate motion was judged to be 5 mm. The extent of intrafraction motion was much smaller than that of interfraction motion. Linear regression analysis showed very little correlation between the two types of motion (r = 0.014, 0.029, and 0.191, respectively) in the RL, AP, and SI directions. CONCLUSION: Using an ultrasound-based system, intrafraction prostate motion occurred predominantly in the anterior and superior directions, but was clinically insignificant. Intrafraction motion was much smaller than interfraction motion, and the two types of movement did not correlate.     

Combined error of patient positioning variability and prostate motion uncertainty in 3D conformal radiotherapy of localized prostate cancer

: TO measure the patient positioning and prostate motion variability and to estimate its influence on the calculated 3D dose distribution in 3D conformal radiotherapy of patients with localized prostate carcinoma.

: Patient positioning variability was determined retrospectively by comparing weas determined by 107 computed tomography (CT) examinations with a CT simulator in 28 patients during radiotherapy.

: In each observed direction, the patient positioning variability and prostate motion showed a normal distribution. This observation enabled the calculation of a combined error of both components. The standard deviation (1 SD) of the patient positioning error in three directions ranged 3.1 to 5.4 mm; the prostate motion variability was significantly greater in the anterior-posterior direction (1 SD = 2.8 mm) than in the mediolateral direction (1 SD = 1.4 mm). The 1 SD of the estimated combined error was in the anterior-posterior direction 6.1 mm and in mediolateral direction 3.6 mm.

: The range of patient positioning variability and prostate motion statistically predictable under the patient setup cnditions used. Dose-volume histograms demonstrating the influence of the combined error of both components on the calculated dose distribution are presented.     

Daily electronic portal imaging of implanted gold seed fiducials in patients undergoing radiotherapy after radical prostatectomy

PURPOSE: The aim of this study was to measure interfraction prostate bed motion, setup error, and total positioning error in 10 consecutive patients undergoing postprostatectomy radiotherapy. METHODS AND MATERIALS: Daily image-guided target localization and alignment using electronic portal imaging of gold seed fiducials implanted into the prostate bed under transrectal ultrasound guidance was used in 10 patients undergoing adjuvant or salvage radiotherapy after prostatectomy. Prostate bed motion, setup error, and total positioning error were measured by analysis of gold seed fiducial location on the daily electronic portal images compared with the digitally reconstructed radiographs from the treatment-planning CT. RESULTS: Mean (+/- standard deviation) prostate bed motion was 0.3 +/- 0.9 mm, 0.4 +/- 2.4 mm, and -1.1 +/- 2.1 mm in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) axes, respectively. Mean set-up error was 0.1 +/- 4.5 mm, 1.1 +/- 3.9 mm, and -0.2 +/- 5.1 mm in the LR, SI, and AP axes, respectively. Mean total positioning error was 0.2 +/- 4.5 mm, 1.2 +/- 5.1 mm, and -0.3 +/- 4.5 mm in the LR, SI, and AP axes, respectively. Total positioning errors >5 mm occurred in 14.1%, 38.7%, and 28.2% of all fractions in the LR, SI, and AP axes, respectively. There was no significant migration of the gold marker seeds. CONCLUSIONS: This study validates the use of daily image-guided target localization and alignment using electronic portal imaging of implanted gold seed fiducials as a valuable method to correct for interfraction target motion and to improve precision in the delivery of postprostatectomy radiotherapy.     

An evaluation of intrafraction motion of the prostate in the prone and supine positions using electromagnetic tracking

Purpose

To evaluate differences in target motion during prostate irradiation in the prone versus supine position using electromagnetic tracking to measure prostate mobility.

Materials/methods

Twenty patients received prostate radiotherapy in the supine position utilizing the Calypso Localization System® for prostate positioning and monitoring. For each patient, 10 treatment fractions were followed by a session in which the patient was repositioned prone, and prostate mobility was tracked. The fraction of time that the prostate was displaced by >3, 5, 7, and 10 mm was calculated for each patient, for both positions (400 tracking sessions).

Results

Clear patterns of respiratory motion were seen in the prone tracks due to the influence of increased abdominal motion. Averaged over all patients, the prostate was displaced >3 and 5 mm for 37.8% and 10.1% of the total tracking time in the prone position, respectively. In the supine position, the prostate was displaced >3 and 5 mm for 12.6% and 2.9%, respectively. With both patient setups, inferior and posterior drifts of the prostate position were observed. Averaged over all prone tracking sessions, the prostate was displaced >3 mm in the posterior and inferior directions for 11.7% and 9.5% of the total time, respectively.

Conclusions

With real-time tracking of the prostate, it is possible to study the effects of different setup positions on the prostate mobility. The percentage of time the prostate moved >3 and 5 mm was increased by a factor of three in the prone versus supine position. For larger displacements (>7 mm) no difference in prostate mobility was observed between prone and supine positions. To reduce rectal toxicity, radiotherapy in the prone position may be a suitable alternative provided respiratory motion is accounted for during treatment. Acute and late toxicity results remain to be evaluated for both patient positions.